Anopheles gambiae and other insects utilize a variety of strategies to combat microbial invaders. The long-term goal of the PIs research is to characterize and understand the mechanisms of innate immunity used by the mosquito against microbes. This proposal focuses on the particular role of the Down syndrome cell adhesion molecule (Dscam) as a hypervariable immune surveillance receptor. Dscam's complex genomic organization and remarkable properties suggest that it plays multiple roles in immune defense: In A. gambiae, alternative splicing of the AgDscam gene produces >31,920 alternative splice- form receptors with different adhesive characteristics and specificities. AgDscam produces microbe-specific splice-form repertoires upon immune challenge and is involved in both antibacterial and anti-Plasmodium defense. The studies outlined here will further test the hypothesis that, as previously shown for challenge with a limited number of bacteria, this phenotypic plasticity of the AgDscam gene allows it to produce receptor molecules with potent antimicrobial activity and high affinity for bacteria and the Plasmodium parasite. To test this hypothesis, the proposed studies will use RNAi silencing, immunohistochemical staining, microarray analyses, and interaction analyses to determine (in Specific Aim 1) the regulation of AgDscam splicing and production of splice form repertoire by microbe challenge and the innate immune pathways, and (in Aims 2) the specific splice-form repertoires involved in these defenses and interactions with microbes. We will finally test the anti-Plasmodium defense specificity and efficacy of AgDscam in genetically modified mosquito lines that over-express pathogen specific splice forms (in Specific Aim 3). These analyses will elucidate one of the most remarkable players of the insect innate immune system, which allows it to cope with a broad spectrum of microbes through the microbe challenge specific production of pattern recognition receptors. The study will also assess the feasibility to use AgDscam for the generation of Plasmodium resistant mosquitoes that could be used for the development of a malaria control strategy.